The present invention relates to a solid golf ball, particularly a solid golf ball having a solid core, such as a two-piece golf ball or a multi-piece golf ball of three or more pieces. The invention also relates to a method of manufacturing such a golf ball.
In order to respond to the diverse needs of the market, the production of solid golf balls having a core and a cover at a manufacturing plant has generally entailed fabricating at the same time many types of golf balls of differing performance attributes such as distance and controllability. From a production control standpoint, a preformed body (either a core or a core having an intermediate layer formed thereon) fabricated prior to formation of the cover is often transferred to a temporary storage place following fabrication and stored until such time as the cover is formed. A preformed body that matches a particular cover to be formed is then selected from among a plurality of types of preformed bodies stored at the temporary storage place, and is supplied to the cover-forming step.
In such cases, selection of the preformed body to be supplied to the cover-forming step is facilitated by including a colorant within or coating a colorant on the preformed body so as to impart color to the body, and having the color of the preformed body differ for each type of ball. Even when a core has been colored in this way, by forming an ordinary white cover over the core, the coloration of the core is completely hidden and does not affect the appearance of the golf ball.
Also, when golf ball cores are obtained by molding and vulcanizing a rubber composition containing a base rubber and an unsaturated carboxylic acid, a vulcanized rubber powder is sometimes included in the rubber composition for such purposes as to enhance stability and adjust the rebound and hardness (see Japanese Patent No. 2652502).
Here, in the golf ball manufacturing operation, vulcanized rubber powder that arises during the surface grinding of cores which have been molded and vulcanized is collected and added to the above rubber composition, whereupon the molding and vulcanization of cores is also carried out. The grinding up and use of the cores of discarded golf balls has also been described (JP-A 2002-102388). In addition, the removal of water-soluble unsaturated carboxylic acids such as acrylic acid, methacrylic acid and salts thereof, as well as other water-soluble monomers and polymers, by liquid-washing vulcanized rubber powder obtained from discarded golf balls, and the use of the resulting washed rubber powder, has also been described (see JP-A 2008-253757).
However, in the case of preformed bodies such as the above-described colored cores, the abraded powder or ground powder obtained from such bodies is also colored. When such powder is added as vulcanized rubber powder to a core, the resulting core will of course be colored. As noted above, there is no particular problem in cases where an ordinary white cover is formed over the core. However, when a cover having a yellow color, for example, is formed over the core in order to produce a so-called colored ball, the color tone of the ball may be affected and undesirably altered by the color of the core. In particular, golf balls have been recently described in which a transparent or translucent resin is used to form the cover, or in which pigment is compounded in a transparent or translucent resin to create a ball that exhibits a vibrant color with a sense of transparency. In such golf balls, no coloration whatsoever of the core is allowable.